In general, when compared to other semiconductor devices, Gallium Nitride (GaN)-based high electron mobility transistors (HEMTs) can produce superior RF power densities. The superior performance is due to a high breakdown voltage, low channel resistance, high carrier density, as well as high saturation velocities and a lateral layout allowing for a short gate design. Additionally, the ability of GaN-based HEMTs to operate at high ambient temperatures makes them attractive for many practical applications.
Currently, use of GaN-based Heterostructure Field Effect Transistors (HFETs), such as metal-oxide-semiconductor HFETs (MOSHFETs), metal-insulator-semiconductor HFETs (MISHFETs), and modifications thereof, as RF power amplifiers is limited by the operating stability and self-heating effects of the HFETs. In particular, the operating stability of a state-of-the-art GaN-based HFET is very sensitive to the operating conditions, such as a maximum drain bias, instant peak and average gate voltages, and self-heating effects. In order to minimize the self-heating effects, as well as for energy conservation, it is important to achieve high efficiency operation of the HFET.
However, traditional approaches of enhancing the operating efficiency require specific operating conditions that reduce the stable operation time of the HFET. In particular, the stable operation time for the HFET can drop from thousands of hours to minutes or seconds, even just a few RF cycles.